When applied topically, sunscreen compositions impart a film that protects skin against the damaging effects of exposure to sun's ultraviolet radiation (UVR). Sunscreen actives work on skin's surface by absorbing UVR before it can interact with and damage skin. For maximum skin protection, sunscreen actives must be photostable, maintaining their ability to absorb UVR throughout periods of sun exposure. When sunscreen actives lose their ability to absorb UVR, they become less photoprotective, as more UVR passes thru the protective film to reach underlying skin.
Several sunscreen actives display signs of photoinstability, with perhaps the best-known example being avobenzone, a UVA sunscreen active. Avobenzone's potential to photodegrade represents a major disadvantage in formulation of sunscreen compositions that provide sustained UVA protection during periods of sun exposure. However, in recent years, avobenzone's disadvantage has been overcome by adopting formulation strategies that minimize photodegradation of avobenzone. These strategies include omission of ingredients that are photochemically incompatible with avobenzone (for example, octinoxate) or inclusion of ingredients that help stabilize avobenzone in the presence of UVR. Thus, it is now possible to formulate sunscreen compositions containing avobenzone that provide effective, durable UVA protection to skin over the entire time course of sun exposure.
As a UVB sunscreen active, octyl triazone also shows signs of photoinstability when irradiated with UVR. We have now discovered, surprisingly, that addition of diethylhexyl syringylidene malonate to sunscreen compositions containing octyl triazone significantly enhances octyl triazone's stability during UVR exposure.